集成直流故障换流电路的改进型混合MMC

Improved Hybrid MMC Integrated with DC Fault Commutated Circuit

基于全桥(FB)与半桥(HB)子模块的传统混合式模块化多电平换流器(MMC)是典型的具有直流故障自清除能力的MMC。然而,常规混合MMC中FB占比通常大于50%,增加了成本与损耗。鉴于此,为了减少混合MMC中FB的数量,提出一种集成晶闸管开关电容直流故障换流电路的改进型混合MMC。所提MMC中HB-MMC与FB-MMC均保留了各自完整的主体,并在交流侧采用三绕组变压器进行连接,在直流侧进行串联连接。同时,由于直流侧集成了一个基于晶闸管的开关电容结构,所提MMC能够实现直流故障的清除。研究表明,所提MMC中FB占比可降低至10%~25%,甚至更低(限制于交流电压的波形),在降低换流器成本的同时降低了通态损耗。仿真结果验证了分析的正确性。

Based on full-bridge(FB)and half-bridge(HB)sub-modules(SMs),the conventional hybrid modular multievel converter(MMC)is a typical topology of MMC with DC fault clearing ability.However,the proportion of FB SMs in conventional hybrid MMC is usually greater than 50%,so as to increase the cost and losses.To solve this mentioned issue,a DC fault commutated circuit based on thyristor-switched capacitor(TSC)structure in the hybrid MMC was integrated to reduce the number of FBs,the improved TSC-hybrid MMC was proposed in follows.In TSC-hybrid MMC,HB-MMCs and FB-MMCs were both retained their complete commutated body,and meanwhile,they were connected by a three-winding transformer in AC side and in series with DC side.In particularly,a thyristor-switched capacitor structure was integrated in the DC side of TSC-hybrid MMC to clear the DC fault.According to the analysis,the proportion of FB SMs in TSC-hybrid MMC can be reduced to 10%~25%or even lower(the AC-side voltage quality is a main limiting condition),the cost is reduced as well as the on-state losses.Simulation results validate the correctness of analyses.